Integrated circuits, IC's, are usually in the form of a thin rectangular plastic box with leads to appropriate points of the circuit within the box emerging perpendicularly from opposite sides thereof at points along straight parallel lines formed by the mold line between the top and bottom halves of the box. Intermediate portions of the leads that adjoin the portions emerging from the box are respectively bent at the same angle in planes perpendicular to the plane formed by the parallel lines, and the outer ends of the leads are bent outwardly in a plane parallel to the latter plane to form feet that are to be electrically and physically attached to appropriate points on a flat printed circuit board. Such a structure is illustrated in FIG. 1.
IC's are generally loosely packaged end to end in a transport tube with their feet facing parallels opposing inner walls. At a factory, feeders are provided for conveying the IC's from the transport tube to a pick-up pad from which they are carried by a programmed machine to appropriate positions on a circuit board.
There are two basic types of feeders. The first type has a built in magazine into which the components are transferred from the transportation tube and from which they are fed to the pick-up pad by either gravity or vibratory action or a combination of both. The second type of feeder has no magazine, and after the transport tube is attached to a bar by spring clips, the components are fed to the pick-up pad by vibrating action.
In both types of feeders, the feet at the ends of the electrical leads are used to guide the components onto the pick-up pad. The feet are very frequently rough and sharp. When the sharp feet contact the internal walls of a feeder, there is a strong tendency for them to dig in and cause a jam. Furthermore, the spacing between the feet on one side of the integrated circuit and the feet on the other is not held to a very close tolerance, so that for components having a smaller dimension there is sometimes enough excess clearance between the feet and the internal walls of the feeder to permit the integrated circuit to rotate a few degrees and increase the severity of the jam.
Any jams in the feeder are a serious problem for automatic `pick and place` assembly machines because of `missed pick` problems. Even with constant monitoring by the machine operator, it is impossible to achieve a satisfactory level of efficiency and reliability.